Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum.
We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 microm long and hexaoctahedral prisms up to 1.4 microm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability--a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming--drove diversification of magnetite-forming organisms, likely including eukaryotes.
Schumann
Dirk
D
Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, QC, Canada H3A 2A7.
Raub
Timothy D
TD
Kopp
Robert E
RE
Guerquin-Kern
Jean-Luc
JL
Wu
Ting-Di
TD
Rouiller
Isabelle
I
Smirnov
Aleksey V
AV
Sears
S Kelly
SK
Lücken
Uwe
U
Tikoo
Sonia M
SM
Hesse
Reinhard
R
Kirschvink
Joseph L
JL
Vali
Hojatollah
H
D000538:Aluminum Silicates / Q000032:analysis; D000077215:Clay; D004777:Environment; D052203:Ferrosoferric Oxide / Q000737:chemistry* / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology; D049690:History, Ancient; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010103:Oxygen Isotopes; D013997:Time Factors
D000538:Aluminum Silicates; D010103:Oxygen Isotopes; D000077215:Clay; D052203:Ferrosoferric Oxide